Electrochemical fuel cells are an attractive power source for electric vehicles, including wheeled vehicles, trains, marine vessels and airborne vehicles. Electrochemical fuel cells convert a fuel and an oxidant to produce electric power which can be used to power an electric propulsion motor in a vehicle. Thus, in a fuel cell engine, fuel- and oxidant-containing reactant streams are supplied to a fuel cell stack in order for it to operate. Typically a coolant fluid stream is also supplied to the fuel cell stack. Fuel cell stacks typically include inlet ports and manifolds for directing a fuel stream and an oxidant stream to the anode and cathode, respectively, and corresponding exhaust manifolds and outlet ports for expelling unreacted fuel and oxidant streams and reaction products. Stacks also usually include an inlet part and manifold for directing a coolant fluid to interior channels within the stack, as well as an exhaust manifold and outlet port for coolant fluid exiting the stack. As used herein, the term fuel cell stack refers to a plurality of fuel cells, regardless of the nature of their configuration or electrical interconnection.
In conventional fuel cell powered wheeled vehicles, one or more fuel cell stacks are used to electrically power an electric propulsion motor which is directly coupled, optionally via a speed reducer (single or multiple ratio transmission), to the vehicle drive shaft. In addition, the fuel cell stack provides independent electric power to numerous separate motors which drive auxiliary devices including pumps and heaters, such as, for example an oxidant air compressor, fuel pump, power steering pump, air brake compressor, air conditioning compressor, cooling fans, and the like. Typically, when the vehicle is stationary, the propulsion motor does not rotate, and therefore auxiliary devices cannot be driven by the propulsion motor when the vehicle is stationary.
The separate motors for the auxiliary devices add significantly to the weight, volume, cost and complexity of a fuel cell engine. In particular, each motor in the system generally requires a motor controller or inverter (for example, for each synchronous AC motor) and associated control system, thus many duplicate components and subassemblies are required.
A fuel cell engine and its associated control systems can be simplified considerably by coupling the propulsion motor to mechanically drive one or more auxiliary devices in the vehicle.
It is particularly advantageous to couple the stream to the fuel cell stack. For example, when the propulsion motor is coupled to drive a device for directing a reactant stream into the fuel cell stack a synergistic effect arises which can simplify and stabilize the engine control system. The electrical power output of a fuel cell stack is related to the rate of supply of fuel and oxidant to the fuel cells of the stack. As the vehicle requires more propulsive power the propulsion motor (at any specific torque) will demand more electric power from the fuel cell stack to increase its speed. As the speed of the propulsion motor increases so will the speed of a reactant supply device mechanically coupled to it, thus increasing the rate of reactant delivery to the stack in concert with the demand for increased electrical power output.
Similarly with stack cooling fluids, an inherent increase in the rate of coolant circulation as the propulsion motor demands more electric power, may be beneficial. One or more of the fuel cell stack cooling pumps may be coupled to be driven by the propulsion motor. Typically the stack generates more heat as it produces more power so, provided the increased rate of coolant circulation results in greater cooling, this arrangement can be advantageous.